The invention is related generally to the field of centralizers, such as used on casing inserted in wellbores drilled through the earth. More specifically, the invention is related to centralizers which can pass through an opening that is smaller than the opening in which a device is to be centralized.
Wellbores drilled through the earth to extract petroleum and the like are commonly xe2x80x9ccompletedxe2x80x9d by cementing a steel pipe or casing in the wellbore after it is drilled. The casing serves to maintain the mechanical integrity of the wellbore, provides a conduit for produced fluids to move to the earth""s surface, and hydraulically isolates earth formations from each other so that high fluid pressure earth formations do not discharge fluid into lower fluid pressure earth formations.
The casing is typically inserted into the drilled wellbore by coupling segments of the casing together and lowering the coupled segments into the wellbore. To cement the casing in place in the wellbore, cement is typically pumped through the interior of the casing, and is discharged into an annular space between the casing and the wellbore from the bottom of the casing. An important aspect of properly cementing the casing in place to complete a wellbore is that the casing have a substantially uniform annular space around it at all places along the length of the wellbore. Uniformity of the annular space increases the likelihood that the cement will completely and uniformly fill the annular space, thereby ensuring that the wellbore properly hydraulically isolates earth formations from each other. Uniformity of the annular space is affected by the trajectory of the wellbore and the final shape of the wellbore, among other factors. Frequently wellbores are drilled along trajectories other than vertical, so earth""s gravity and bends in the wellbore cause the casing to rest on the wall of the wellbore in some places along the wellbore. In other cases, the wall of the wellbore may include out of round sections, for example washouts or keyseats, which make cementing operations more difficult.
It is known in the art to use centralizers to keep the casing as close as possible to the center of the wellbore for proper cementing. Typical centralizers known in the art are shown, for example, in a sales brochure published by Antelope Oil Tool and Manufacturing Company, Mineral Wells, Tex. (not dated). Centralizers are typically coupled to the exterior surface of the casing at selected locations along the casing prior to inserting the casing into the wellbore. Blades on the centralizers provide a restoring force which tends to push the casing into the center of the wellbore. Specifications for the amount of restoring force, and proper use of centralizers are described in a document entitled, Specifications for Bow-Spring Centralizers, API Specification 10D, fifth edition, American Petroleum Institute, Washington, D.C. (1994). Generally speaking, casing centralizers are made to center a particular outside diameter (OD) casing within a particular nominal diameter wellbore. The casing OD is selected by the wellbore operator to closely match the wellbore diameter, which primarily related to the diameter of the drill bit used to drill that segment of the wellbore.
More recently, it has become known in the art to drill wellbores to a depth greater than a depth to which casing has been set, in which the greater depth portion of the wellbore has a diameter larger than the diameter of the casing. This type of drilling can be performed using various types of reaming tools such as hydraulic underreamers or specialized drill bits known as bi-center bits. See, for example, U.S. Pat. No. 6,036,131 issued to Beaton. Drilling this type of wellbore makes it possible to insert a larger completion device in the deeper portion of the wellbore, such as gravel pack or sand screens, than would be possible using conventional drilling techniques. Completing wellbores having such deeper sections including oversize diameters using centralizers known in the art has proven difficult because it is impracticable to move a larger outside diameter centralizer through a smaller internal diameter casing or other opening.
It is desirable to have a centralizer which can position a casing inside a larger diameter wellbore than the opening through which the centralizer can freely pass.
The invention is a centralizer for laterally positioning an instrument in an opening larger in diameter than a diameter of an opening through which the centralizer can freely pass. A plurality of spring blades extend substantially axially between a fixed position along the instrument to a rotatable stop collar at another axial position along the instrument A latch is operatively coupled to the stop collar the instrument surface, and is adapted to enable rotation of the stop collar about the instrument upon release of the latch.
In one embodiment, the latch includes a control latch pivotally coupled at one end to the outer surface of the instrument and releasably locked to the outer surface of the instrument at its other end. The latch according to this embodiment includes a responding latch pivotally operationally coupled to the outside surface of the instrument. The responding latch is operatively engaged with the control latch at one end and is operatively engaged to the stop collar at the other end. The control and responding latches have pivot positions selected so that a force applied by locking the control latch is substantially less than a force applied by the stop collar to the responding latch.